Webb telescope traces record-distant fast radio burst to a young, faint galaxy 10 billion years away

The detection

Astronomers using the MeerKAT radio telescope in South Africa detected a fast radio burst on 4 March 2024, using a system called MeerTRAP that is designed to catch fast-changing radio signals from space in real time. The burst, dubbed FRB 20240304B, showed a large amount of dispersion, meaning its frequencies arrived at slightly different times after passing through electrically charged material in space. That measurement indicated the signal had come from a great distance. The researchers report that the burst was produced when the universe was only about 3 billion years old, and that it has travelled through approximately 80% of cosmic history. The burst is believed to be the farthest fast radio burst detected so far, more than double the previous distance record. The study, led by Manisha Caleb and Themiya Nanayakkara of the University of Sydney, was published in Science.

Locating the source

When the team pointed large ground-based telescopes, including the Keck Telescopes, at the burst's position on the sky, they could not see a host galaxy because it was simply too faint. The team then turned to the James Webb Space Telescope, whose infrared camera revealed a tiny galaxy very close to the position of the burst. La Razón reports that the galaxy lies within a few tenths of an arcsecond of the burst's position and that the association has a probability of 97.5%. The researchers broke the galaxy's light into its spectrum and measured how its frequencies had shifted. That shift allowed them to calculate how fast the galaxy is moving away from us because of the expansion of the universe, and from that, how old it is. These calculations confirmed that the light was emitted 10.6 billion years ago.

What the galaxy reveals

The host galaxy turned out to be a surprise in its own right. According to the research summary, it contains only about 10 million times the mass of the Sun, a tiny fraction of the mass of the Milky Way. Data from the James Webb telescope indicated that the burst came from a young, very small galaxy forming stars at a very high rate, with few metals around it. Engadget notes that the galaxy is also small and young compared with the galaxies that produced earlier bursts, which were found billions of years later in massive, star-forming galaxies. The galaxy existed when star formation was at its peak in the universe.

Competing explanations

One leading theory holds that fast radio bursts are generated when two neutron stars merge. Engadget points out that such collisions take billions of years, which would mean bursts from mergers can only come from older galaxies. Another theory proposes that bursts come from massive stars that explode in a supernova and leave behind magnetars, which are neutron stars with very powerful magnetic fields. Caleb said the work points toward a supernova origin.

Our work suggests that it's very unlikely that this [fast radio burst] was produced by a merger.

Nanayakkara said the finding constrains any explanation of how the burst was produced.

Whatever the mechanism that causes this radio burst has to account for that fact that it can be produced in... very young galaxies with very low amount of metals.

What remains open

More than 10,000 fast radio bursts have been detected since 2007, when the first one was observed with a large radio dish in Australia. Nanayakkara said some repeat continuously, some repeat for a while and then stop, and some are seen only once. Whether this distant burst will produce further signals remains to be seen. Joeri van Leeuwen of the Astron radio astronomy institute in Dwingeloo, who was not involved in the discovery, called the result important for the field.

This beautiful new result broadens our horizon enormously.

Bursts from such distant sources could also help map the thin matter between galaxies, because that matter leaves a signature in the radio emission. Mapping that matter would require many more distant bursts, which van Leeuwen expects will be discovered in the future.